In a structure for driving an LCD, there are two methods for setting a Gamma voltage output value. One method is to externally hang a programmable Gamma calibration chip (P-Gamma IC) to set a Gamma voltage output value by a digital mode, and the other method is that a resistor string is used and a voltage which is output by an external multi-channel operational amplifier (OP) or internal independent OP(s) of a source driver is used as a Gamma voltage. The first method increases the occupied area of the P-Gamma IC on the C/B PCB, and the second method cannot directly and quickly change the Gamma voltage, which needs to select rework resistance values.